1. Field of the Invention
The present invention is directed to a two compartment syringe and more particularly to a two compartment syringe provided with a so-called by-pass.
2State of the Art
Injectable medicaments often show a rapid loss of potency when they are in their ready to use form.
A solution of this problem is found in applying a two compartment syringe system, one compartment containing the solid medication (either in powder form or preferably in lyophilized form) and the other compartment containing the injection fluid. The oldest two compartment system usually consists of two vials with pierceable stoppers. However, this two vials system commonly presents problems with respect to sterility since only the interior of the vials are sterile and bacteria from the exterior of the vials may easily be introduced into the medication during the mixing procedure.
The two compartment syringes as described in U.S. Pat. No. 2,607,344 and South African Pat. No. 84 04 195 therefore embody a major improvement over the two vial system.
The above-mentioned South African patent more particularly discloses a two compartment medication syringe that comprises:
1. a barrel having a chamber for retaining medication;
2. a tip extending from a distal end of said barrel having a passageway therethrough communicating with said chamber, said tip including means for accepting a hypodermic needle;
3. a by-pass stopper slidably positioned in fluid-tight engagement inside said barrel;
4. A raised peripheral portion of said barrel serving as a by-pass and defining a by-pass zone, said by-pass zone being longer along the longitudinal axis of said barrel than the length of said by-pass stopper along the longitudinal axis of said barrel, said by-pass positioned so that when said by-pass stopper is within said by-pass zone, the volume defined within said chamber between said by-pass stopper and said distal end of said barrel is approximately the volume of the combined components of the medication, said by-pass being raised enough to allow fluid flow around said by-pass stopper when said by-pass stopper is positioned within said by-pass zone; and a stopper slidably positioned in fluid-tight engagement inside said barrel adapted to engage a plunger rod to facilitate its operation, said stopper capable of moving fluid from said chamber through said passageway upon its movement toward said distal end.
This syringe minimizes sterility problems by allowing the mixing and administering steps to be performed without puncturing stoppers or transferring the medication compounds through surfaces which are exterior to the syringe assembly.
The medication syringe according to the South African patent has a compartment defined by the tip and the by-pass stopper, and a second compartment defined by the by-pass stopper and the stopper adapted to engage the plunger rod. Hereinafter compartment A will be called the "needle-compartment" and compartment B the "plunger-compartment" indicating the relative position of the compartments in the barrel.
The needle compartment of the syringe according to the South African patent is intended to contain the solid lyophilized medicament and consequently the plunger compartment is filled up with the injection fluid. This syringe is, indeed, very suitable because lyophilization of the medicament can be carried out directly in the needle compartment itself.
The medication syringe according to the South African patent is, however, less suitable or even unsuitable for use if the injection fluid is to be stored in the needle compartment and the solid or lyophilized medicament in the plunger compartment, because efficient mixing of the two components is impossible.
Under certain circumstances it is easier from a manufacturing point of view or even desired to fill the needle compartment with the injection fluid and to sterilize the syringe and then afterwards to add the medication either in powder or in lyophilized form aseptically into the plunger compartment.